Actuator assembly having dual sensors for detecting the vibration on magnetic disk device

ABSTRACT

According to one embodiment, a magnetic disk device includes a base that includes a bottom wall and side walls standing along a circumference of the bottom wall, a housing that includes a cover facing the bottom wall and closing the base, an actuator assembly that is housed inside the housing and is rotatable around a rotation axis, a head movably supported by the actuator assembly, a control circuit board provided outside of the housing, a first sensor disposed on the control circuit board, and a second sensor disposed inside the housing.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is continuation of application Ser. No. 16/111,782filed Aug. 24, 2018 which is based upon and claims the benefit ofpriority from Japanese Patent Application No. 2018-042312, filed Mar. 8,2018, the entire contents of which are incorporated herein by reference.

FIELD

Embodiments described herein relate generally to a magnetic disk device.

BACKGROUND

A magnetic disk device, for example, a hard disk drive (HDD) generallyincludes a magnetic disk disposed in a housing, a spindle motorsupporting and rotating the magnetic disk, an actuator assemblysupporting a magnetic head, a voice coil motor driving the actuatorassembly, a printed circuit board, and the like.

The magnetic disk device vibrates due to a disturbance, for example, asound pressure, generated from a fan installed outside the magnetic diskdevice. When the magnetic disk device vibrates as described above, it islikely that a positioning error of the magnetic head mounted on theactuator assembly will be increased.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded perspective view showing an internal structure ofa magnetic disk device according to a first embodiment;

FIG. 2 is a view showing an example of change amounts in positioningerrors of the respective heads when the magnetic disk device vibrates atthe respective frequencies;

FIG. 3 is a schematic view showing an example of an actuator assemblywhen the magnetic disk device vibrates at a frequency of 4.8 kHz shownin FIG. 2;

FIG. 4 is a schematic view showing an example of an actuator assemblywhen the magnetic disk device 1 vibrates at a frequency of 6.3 kHz ormore to 9 kHz or less shown in FIG. 2;

FIG. 5 is a schematic view showing an example of a disposition ofsensors in the magnetic disk device 1;

FIG. 6 is a plan view showing an example of a disposition of the sensorsin the magnetic disk device 1;

FIG. 7 is a perspective view of the actuator assembly and a flexibleprinted circuit (FPC) unit viewed from one side;

FIG. 8 is a cross-sectional view showing a configuration example of themagnetic disk device taken along line VIII-VIII shown in FIG. 6;

FIG. 9 is a view showing an example of a positioning control system ofthe head according to the first embodiment; and

FIG. 10 is a view showing an example of a positioning control system ofa head according to a modified example.

DETAILED DESCRIPTION

In general, according to one embodiment, a magnetic disk devicecomprises: a base that comprises a bottom wall and side walls standingalong a circumference of the bottom wall; a housing that comprises acover facing the bottom wall and closing the base; an actuator assemblythat is housed inside the housing and is rotatable around a rotationaxis; a head movably supported by the actuator assembly; a controlcircuit board provided outside of the housing; a first sensor disposedon the control circuit board; and a second sensor disposed inside thehousing.

Hereinafter, embodiments will be described with reference to thedrawings. It should be noted that the drawings are an example, and donot limit the scope of the invention.

First Embodiment

FIG. 1 is an exploded perspective view showing an internal structure ofa magnetic disk device 1 according to a first embodiment.

The magnetic disk device 1 has a housing 10 having a substantiallyrectangular shape. The housing 10 has a base 12 with an opened uppersurface and a rectangular box shape, an inner cover 14 screwed to thebase 12 by a plurality of screws 13 and closing an upper end opening ofthe base 12, and an outer cover (a top cover) 16 disposed to overlap theinner cover 14 and having a circumferential portion welded to the base12. Hereinafter, a direction toward the inner cover 14 and the outercover 16 will be referred to as upward direction (or simply upward), anda direction opposite to the upward direction will be referred to as adownward direction (or simply downward). The base 12 has a bottom wall12 a facing the inner cover 14 with a gap therebetween and having arectangular shape and side walls 12 b standing along a circumference ofthe bottom wall 12 a. The base 12 is integrally molded by, for example,aluminum. The side walls 12 b include a pair of long side walls facingeach other and a pair of short side walls facing each other. A fixingrib 12 c having a substantially rectangular frame shape protrude onupper end surfaces of the side walls 12 b.

The inner cover 14 is formed in a rectangular plate shape using, forexample, stainless steel. A circumferential portion of the inner cover14 is screwed to upper surfaces of the side walls 12 b of the base 12 bythe screws 13, and fixed to an inner side of the fixing rib 12 c. Theouter cover 16 is formed in a rectangular plate shape by, for example,aluminum. The outer cover 16 is formed to have a plane dimensionslightly larger than that of the inner cover 14. The outer cover 16 iswelded to the fixing rib 12 c of the base 12 over the entirecircumferential portion thereof, such that it is air-tightly fixed.

The housing 10 is provided with a plurality of magnetic disks, forexample, five to nine magnetic disks (hereinafter, simply referred to asdisks) 18 as recording media, and a spindle motor 20 as a drivingsection supporting and rotating the disks 18. The spindle motor 20 isdisposed on the bottom wall 12 a. The respective disks 18 have magneticrecording layers provided on upper and/or lower surfaces thereof. Therespective disks 18 are coaxially fitted into a hub (not shown) of thespindle motor 20, and are clamped by a clamp spring and fixed to thehub. As a result, the respective disks 18 are supported in a state inwhich they are located in parallel with the bottom wall 12 a of the base12. The disk 18 rotates at a particular revolution per minute (RPM) bythe spindle motor 20.

In the present embodiment, the five to nine disks 18 are housed in thehousing 10, but the number of the disks 18 is not limited thereto. Inaddition, a single disk 18 may also be housed in the housing 10.

The housing 10 are provided with a plurality of magnetic heads(hereinafter, simply referred to as heads) 17 writing and readinginformation to and from the disks 18 and an actuator assembly (actuator)22 movably supporting these heads 17 with respect to the disks 18. Inaddition, the housing 10 is provided with a voice coil motor(hereinafter, referred to as a VCM) 24 controlling operations such asrotation and positioning of the actuator assembly 22, a ramp loadmechanism 25 maintaining the head 17 at an unload position at which thehead 17 is spaced apart from the disk 18 when the head 17 moves to theoutermost periphery of the disk 18, and a board unit (a wiring member)21. The board unit 21 is formed of a flexible printed wiring board(FPC). This FPC is electrically connected to the heads 17 and a voicecoil 34 (to be described later) of the VCM 24 through a relay FPC on theactuator assembly 22.

The actuator assembly 22 has a bearing unit 28 that is rotatable, aplurality of arms 32 extending from the bearing unit 28, and suspensionassemblies (suspensions) 30 extending from the respective arms 32. Theheads 17 are supported at tip portions of the respective suspensionassemblies 30. The actuator assembly 22 moves the head 17 to aparticular position on the disk 18 by driving of the VCM 24.

A printed circuit board (a control circuit board) 90 is screwed to anouter surface (a bottom surface) of a bottom wall 12 a of the base 12 bya plurality of screws 23. The control circuit board 90 faces the bottomwall 12 a of the base 12 with a slight gap therebetween. An insulatingsheet (not shown) as an insulating member is disposed between the outersurface of the bottom wall 12 a of the base 12 and the control circuitboard 90. Electronic components such as a semiconductor chip and acontrol section (a controller) 130 are mounted on an inner surface (asurface facing the base 12) of the control circuit board 90. The controlcircuit board 90 has a connector (not shown). This connector iselectrically connected to the FPC unit 21. The control section 130controls an operation of the spindle motor 20, and controls operationsof the VCM 24 and the heads 17 through the board unit 21.

FIG. 2 is a view showing an example of change amounts in positioningerrors of the respective heads 17 when the magnetic disk device 1vibrates at the respective frequencies. FIG. 2 shows increase amounts(hereinafter, referred to as change amounts) in positioning errors ofthe respective heads 17 when the magnetic disk device 1, for example,the housing 10, vibrates due to a disturbance. In FIG. 2, a verticalaxis indicates a change amount, and a horizontal axis indicates therespective heads 17 from an inner cover 14 side (hereinafter, referredto as a cover side) to a bottom wall 12 a side (hereinafter, referred toas a base side). In FIG. 2, it is shown that the positioning errors ofthe respective heads 17 are increased (deteriorated) as the changeamounts increase. Hereinafter, in a region supporting the plurality ofheads 17 by the actuator assembly 22, a region of the cover side issimply referred to as a cover region, a region of the base side isreferred to as a base region, and a region between the cover region andthe base region is referred to as an intermediate region. In addition,heads 17 located in the cover region are referred to as heads 17 of thecover side, heads 17 located in the base region are referred to as heads17 of the base side, and heads 17 located in the intermediate region arereferred to as intermediate heads 17. Due to a disturbance such as asound pressure by a fan for cooling a central processing unit (CPU), orthe like, of a server, the magnetic disk device 1 (the housing 10) canvibrate at a frequency of, for example, 4 to 9 kHz. In FIG. 2, as anexample, a distribution (hereinafter, referred to as a distribution ofchange amounts of 4.8 kHz) D21 of change amounts in positioning errorsfrom the heads 17 of the cover side to the heads 17 of the base sidewhen the magnetic disk device 1 vibrates at a frequency of 4.8 kHz, adistribution (hereinafter, referred to as a distribution of changeamounts of 6.3 kHz) D22 of change amounts in positioning errors from theheads 17 of the cover side to the heads 17 of the base side when themagnetic disk device 1 vibrates at a frequency of 6.3 kHz, and adistribution (hereinafter, referred to as a distribution of changeamounts of 8 to 9 kHz) D23 of change amounts in positioning errors fromthe heads 17 of the cover side to the heads 17 of the base side when themagnetic disk device 1 vibrates at a frequency of 8 to 9 kHz are shown.

As shown by the distribution D21 of the change amounts of 4.8 kHz, whenthe magnetic disk device 1 vibrates at the frequency of 4.8 kHz, changeamounts of the respective heads 17 from the heads 17 on the cover sideto the heads 17 on the base side are substantially constant. As shown bythe distribution D22 of the change amounts of 6.3 kHz and thedistribution D23 of the change amounts of 8 to 9 kHz, when the magneticdisk device 1 vibrates at the frequencies of 6.3 kHz and 8 to 9 kHz,change amounts of the heads 17 of the cover side and the heads 17 of thebase side are larger than those of the intermediate heads 17. When themagnetic disk device 1 vibrates at the frequencies of 6.3 kHz and 8 to 9kHz, the change amounts of the heads 17 of the cover side and the heads17 of the base side are larger than those of the intermediate heads 17.The change amounts of the heads 17 of the cover side and the heads 17 ofthe base side when the magnetic disk device 1 vibrates at thefrequencies of 6.3 kHz and 8 to 9 kHz are larger than those of the heads17 of the cover side and the heads 17 of the base side when the magneticdisk device 1 vibrates at the frequency of 4.8 kHz. The change amountsof the intermediate heads 17 when the magnetic disk device 1 vibrates atthe frequencies of 6.3 kHz and 8 to 9 kHz are larger than those of theintermediate heads 17 when the magnetic disk device 1 vibrates at thefrequency of 4.8 kHz.

FIG. 3 is a schematic view showing an example of the actuator assembly22 when the magnetic disk device 1 vibrates at the frequency of 4.8 kHzshown in FIG. 2. FIG. 3 shows the actuator assembly 22 viewed from thehead 17 side. In FIG. 3, only components required for a description areshown. In FIG. 3, a first direction X, a second direction Z, and a thirddirection Y are orthogonal to each other, but may also intersect witheach other in a state in which they are not orthogonal to each other.Hereinafter, a direction toward a tip of an arrow indicating the firstdirection X will be referred to as a right side (or simply referred toas a right), and a direction from the tip of the arrow indicating thefirst direction X toward the other side will be referred to as a leftside (or simply referred to as a left). The first direction Xcorresponds to a moving direction (hereinafter, also referred to as amovement direction or a translation direction) of each head 17. In thesecond direction Z, a direction toward a tip of an arrow indicating thesecond direction Z is upward, and a direction from the tip of the arrowindicating the second direction to the other side is downward. Inaddition, a length of an object in the second direction Z may also bereferred to as a thickness or a height, and the second direction Z maybe referred to as a thickness direction or a height direction.

As shown in FIG. 3, in the actuator assembly 22, the plurality of heads17 are arranged at intervals in the second direction Z. When themagnetic disk device 1 vibrates at the frequency of 4.8 kHz, therespective heads 17 vibrate in the first direction X. In this case,substantially the same acceleration is applied to each head 17 in thefirst direction X. For this reason, the respective heads 17 aredisplaced by substantially the same distance in the first direction Xwith respect to an axis (hereinafter, referred to as a reference axis)AX0 passing through the bearing unit 28. The reference axis AX0corresponds to, for example, a rotation axis of the actuator assembly22. The reference axis AX0 extends in, for example, the second directionZ, and is substantially perpendicular to the bottom wall 12 a. In theexample shown in FIG. 3, an acceleration in a rightward direction isapplied to the respective heads 17. For this reason, the respectiveheads 17 are displaced to the right side from the reference axis AX0 bysubstantially the same distance X0.

FIG. 4 is a schematic view showing an example of the actuator assembly22 when the magnetic disk device 1 vibrates at a frequency of 6.3 kHz ormore to 9 kHz or less shown in FIG. 2. In FIG. 4, only componentsrequired for a description are shown.

When the magnetic disk device 1 vibrates at the frequency of 6.3 kHz ormore to 9 kHz or less, the respective heads 17 vibrate while twistingaround a node NV of vibration of the actuator assembly 22. Here, thenode NV of vibration includes a portion having a slight amplitudewithout substantially vibrating as well as a portion having an amplitudeof 0 without vibrating. In this case, an acceleration or an angularacceleration is applied to the respective heads 17. For this reason, therespective heads 17 rotate around the node NV in an X-Z plane. In theexample shown in FIG. 4, an acceleration in a rightward direction or anangular acceleration in a clockwise direction is applied to therespective heads 17. For this reason, the respective heads rotate at anangle of θ0 around the node NV of vibration located on the referenceaxis AX0 in the X-Z plane. As shown in FIG. 4, the heads 17 of the coverside and the heads 17 of the base side significantly fluctuate becausedistances up to the node NV are large, and the intermediate heads 17slightly fluctuate because distances up to the node NV are small.

FIG. 5 is a schematic view showing an example of a disposition ofsensors SR1 and SR2 in the magnetic disk device 1. In FIG. 5, onlycomponents required for a description are shown.

At least one of the sensors SR1 and SR2 is disposed inside the housing10, and the other of the sensors SR1 and SR2 is provided outside thehousing 10. The sensors SR1 and SR2 are acceleration sensors detectingaccelerations. For example, one of the sensors SR1 and SR2 may be anacceleration sensor, and the other of the sensors SR1 and SR2 may be anangular acceleration sensor. In the example shown in FIG. 5, the sensorSR1 is located on the inner surface of the control circuit board 90. Thesensor SR2 is located on the board unit 21. The sensor SR1 may belocated at another portion outside the housing 10. The sensor SR2 may bedisposed at a portion other than the board unit 21 at an inner side andan upper side of the housing 10. The sensor SR2 may be located at aninner side and a lower side of the housing 10. In addition, the sensorsSR1 and SR2 may be located at portions other than the portions describedabove as long as they are disposed in a region where a resonance modeother than a disturbance such as a sound pressure hardly occurs, thatis, for example, a region fixed by screws, or the like.

FIG. 6 is a plan view showing an example of a disposition of the sensorsSR1 and SR2 in the magnetic disk device 1. In FIG. 6, only componentsrequired for a description are shown.

In the example shown in FIG. 6, the sensors SR1 and SR2 are arranged ona straight line passing through the bearing unit 28, for example, thereference axis AX0 and are arranged substantially in parallel with amoving direction of the head 17, for example, the first direction X.Hereinafter, a direction in which the sensors SR1 and SR2 are arrangedis referred to as an arrangement direction Xa. Although a case in whichthe sensors SR1 and SR2 are arranged in parallel to the moving directionof the head 17 is described, the sensors SR1 and SR2 may not be inparallel with the moving direction of the head 17 as long as they arearranged along the moving direction of the head 17. The sensors SR1 andSR2 are arranged along the moving direction of the head 17 as describedabove, such that it is possible to easily detect an influence on thehead 17 when the magnetic disk device 1 vibrates at a specificfrequency. The sensor SR1 and the sensor SR2 may not be disposed on thestraight line passing through bearing unit 28 (the reference axis AX0).In addition, the sensors SR1 and SR2 may be arranged in a directionintersecting with the moving direction of the head 17. The sensor SR1 islocated in a region RG1 of the control circuit board 90 screwed by thescrews 23. In addition, the sensor SR1 may be located in another screwedregion of the control circuit board 90 other than the region RG1.

FIG. 7 is a perspective view of the actuator assembly 22 and the FPCunit 21 viewed from one side.

As shown in FIG. 7, the actuator assembly 22 includes an actuator block29 having a through-hole 80, the bearing unit (a unit bearing) 28provided in the through-hole 80 and rotatable, the plurality of arms 32,for example, ten arms 32 extending from the actuator block 29 in thethird direction (hereinafter, also referred to as an extendingdirection) Y, and the suspension assemblies 30 attached to therespective arms 32. The heads 17 are supported by the respectivesuspension assemblies 30 of the actuator assembly 22. The bearing unit28 has a pivot standing on the bottom wall 12 a of the base 12 in thevicinity of outer circumferences of the disks 18, a plurality ofbearings attached to the pivot, a spacer disposed between the bearings,and the like. The plurality of bearings of the bearing unit 28 arefitted into the through-hole 80 of the actuator block 29, and are fixedto the actuator block 29 by an adhesive injected into the through-hole80 or screws (not shown). In this way, the actuator assembly 22 issupported on the bottom wall 12 a so as to be rotatable around the pivotof the bearing unit 28, for example, around the reference axis AX0passing through the pivot.

In the present embodiment, the actuator block 29 and the ten arms 32 areformed integrally with each other using aluminum, or the like, toconstitute a so-called E block. The arms 32 are formed in, for example,an elongated flat plate shape, and extends from the actuator block 29 inthe third direction Y orthogonal to the pivot of the bearing unit 28.The ten arms 32 are arranged in the second direction Z, and are providedin parallel with each other a gap therebetween.

The actuator assembly 22 has a support frame 36 extending from theactuator block 29 in a direction opposite to the arm 32, and the voicecoil 34 constituting a part of the VCM 24 is supported by the supportframe 36. As shown in FIG. 1, the voice coil 34 is located between apair of yokes 38 of which one is fixed onto the base 12, and constitutesthe VCM 24 together with the yokes 38 and a magnet fixed to any of theyokes.

The actuator assembly 22 includes eighteen suspension assemblies 30 eachsupporting the heads 17, and these suspension assemblies 30 are attachedto extending ends 32 a of the arms 32, respectively. A plurality ofsuspension assemblies 30 include up-head suspension assembliessupporting the heads 17 upward and down-head suspension assembliessupporting the heads 17 downward. The up-head suspension assemblies andthe down-head suspension assemblies are configured by disposing thesuspension assemblies 30 having the same structure so that upward anddownward directions of the suspension assemblies 30 are changed.

Each of the suspension assemblies 30 has a base plate 44 having asubstantially rectangular shape, a load beam 46 formed of an elongatedleaf spring, a pair of piezoelectric elements (PZT elements) 47, and aflexure (a wiring member) 48 transferring a write signal, a read signal,and a driving signal of the piezoelectric elements 47 and having anelongated band shape. A base end portion of the base plate 44 is fixedto the extending end 32 a of the arm 32, and is, for example, caulked. Abase end portion of the load beam 46 is overlapped with and fixed to anend portion of the base plate 44. The load beam 46 extends from the baseplate 44, and is tapered toward an extending end. The base plate 44 andthe load beam 46 are formed of, for example, stainless steel. Thepiezoelectric elements 47 finely control an operation of the head 17 byexpansion and contraction operations. Hereinafter, a component includinga control system controlling the piezoelectric elements 47, thepiezoelectric elements 47, wirings connecting the control system and thepiezoelectric elements to each other, and the like, and finely (forexample, more finely than a control by the VCM 24) controlling the head17 may be referred to as a micro actuator (MA).

The flexure 48 has a metal plate (a backing layer) formed of stainlesssteel, which is a base, an insulating layer formed on the metal plate, aconductive layer constituting a plurality of wirings (wiring patterns)formed on the insulating layer, and a protective layer (an insulatinglayer) covering the conductive layer to form a laminate having anelongated band shape.

The flexure 48 has a tip side portion attached onto surfaces of the loadbeam 46 and the base plate 44 and a base end side portion extendingoutwardly from a side edge of the base plate 44 and extending up to thebase end portion (the actuator block 29) of the arm 32 along the sideedge of the base plate 44 and the arm 32. A deformable gimbal portion(an elastic support portion) is provided at a tip portion of the flexure48 located on the load beam 46, and the head 17 is mounted on the gimbalportion. The wirings of the flexure 48 are electrically connected to thehead 17.

The base end side portion of the flexure 48 extends outwardly from theside edge of the base plate 44, and then extends up to the base end ofthe arm 32 along the side edge and one side edge of the arm 32. Aconnection end portion 48 c of the flexure 48 is formed at one end ofthe base end side portion. The connection end portion 48 c is formed inan elongated rectangular shape. The connection end portion 48 c is bentat a right angle to the base end side portion, and is locatedsubstantially perpendicular to the arm 32. The connection end portions48 c is provided with a plurality of connection terminals (connectionpads) 50 arranged in a row. These connection terminals 50 are connectedto the wirings of the flexure 48, respectively. That is, the pluralityof wirings of the flexure 48 extend over substantially the entire lengthof the flexure 48, and each have one end electrically connected to thehead 17 and the other end connected to the connection terminals (theconnection pads) 50 of the connection end portion 48 c.

The FPC unit 21 has a base portion 60 having a substantially rectangularshape, a relay portion 62 extending from one side edge of the baseportion 60 and having an elongated band shape, and a jointing portion 64provided continuously at a tip portion of the relay portion 62 andhaving a substantially rectangular shape, which are formed integrallywith one another. The base portion 60, the relay portion 62, and thejointing portion 64 are formed by a flexible printed circuit board. Theflexible printed circuit board has an insulating layer formed ofpolyimide, or the like, a conductive layer formed on the insulatinglayer and forming wirings, connection pads, and the like, and aprotective layer covering the conductive layer.

Electronic components such as a conversion connector (not shown) and aplurality of capacitors (not shown) are mounted on one surface (an outersurface) of the base portion 60, and are electrically connected towirings (not shown). Each of metal plates 56 and 58 functioning asreinforcing plates are attached to the other surface (an inner surface)of the base portion 60. The base portion 60 is bent by 90 degrees at aportion between the metal plate 56 and the metal plate 58. In addition,in the base portion 60, a pedestal 51 formed of a resin, or the like, isformed on the metal plate 56. The pedestal 51 has protrusion portions 52and 53 protruding upward in the second direction Z. In other words, theprotrusion portions 52 and 53 protrude toward the cover side. A wiring54 and the sensor SR2 are mounted on the protrusion portion 52. Thewiring 54 extends from the outer surface of the base portion 60 to anupper surface 52 s of the protrusion portion 52. The sensor SR2 islocated on the upper surface 52 s of the protrusion portion 52. Thesensor SR2 may be located on an upper surface 53 s of the protrusionportion 53. In addition, the wiring 54 may extend from the outer surfaceof the base portion 60 to the upper surface 53 s of the protrusionportion 53. The wiring 54 has one end portion connected to theconversion connector, or the like, and the other end portion coveringthe upper surface 52 s of the protrusion portion 52. The sensor SR2 isprovided on the wiring 54, and is electrically connected to the wiring54. The protrusion portions 52 and 53 have, for example, the same heightas that of the actuator assembly 22 (the actuator block 29) or a heightbetween a height of the metal plate 58 and the height of the actuatorblock 29. The protrusion portions 52 and 53 may also have a heighthigher or lower than that of the actuator block 29. In addition, theprotrusion portions 52 and 53 may also have a height higher or lowerthan that of the metal plate 58. The base portion 60 is disposed on thebottom wall 12 a of the housing 10, and is screwed to the bottom wall 12a of the housing 10 by two screws SW1 and SW2 each fitted into screwholes formed in the upper surfaces 52 s and 53 s of the protrusionportions 52 and 53. The screw SW1 is fitted into a screw hole formed inthe wiring 54 disposed on the upper surface 52 s and the protrusionportion 52, and the wiring 54 is fixed to the upper surface 52 s of theprotrusion portion 52. The sensor SR2 is located in a region RG2 fixedby the screw SW1 on the wiring 54. The conversion connector on the baseportion 60 is connected to the control circuit board 90 provided on abottom surface side of the housing 10. The relay portion 62 extends fromthe side edge of the base portion 60, turns substantially at a rightangle, and extends toward the actuator assembly 22.

The jointing portion 64 provided at an extending end of the relayportion 62 is formed in a rectangular shape having a width that issubstantially the same as the height (a thickness) of the actuator block29. The jointing portion 64 has a plurality of connection pad groupscorresponding to the connection end portion 48 c of the flexure 48. Ahead IC (a head amplifier) 66 is mounted on the jointing portion 64. Thehead IC 66 is connected to the connection pad groups and the board unit21 through wirings. In addition, the jointing portion 64 has aconnection pad 68 for connecting the voice coil 34 thereto. A backingplate 70 formed of, for example, aluminum is attached as a reinforcingplate to an inner surface (a back surface) of the jointing portion 64.The backing plate 70 is formed to have substantially the same shape andsize as those of the jointing portion 64, and is attached tosubstantially the entire surface of the jointing portion 64.

In the jointing portion 64 configured as described above, the backingplate 70 side is attached to one side surface (an installation surface)of the actuator block 29 extending in the second direction Z and thethird direction Y, and is screwed to the installation surface by twofixing screws 72. The connection end portions 48 c of the respectiveflexures 48 are drawn out to the installation surface of the actuatorblock 29, and are jointed to the jointing portion 64. In addition, awiring of the voice coil 34 is connected to the connection pad 68 of thejointing portion 64.

In this way, eighteen heads 17 are electrically connected to the baseportion 60 through the wirings and the connection end portions 48 c ofthe flexures 48 and the jointing portion 64 and the relay portion 62 ofthe FPC unit 21, respectively. In addition, the base portion 60 isconnected to the printed circuit board on the bottom surface side of thehousing 10 through the conversion connector.

As shown in FIG. 5, in a state in which the actuator assembly 22 and theFPC unit 21 configured as described above are incorporated on the base12, a lower end portion of the pivot of the bearing unit 28 is fixed tothe base 12, and the bearing unit 28 stands substantially in parallelwith a spindle of the spindle motor 20. Each of the disks 18 is disposedbetween two suspension assemblies 30. During an operation of a hard diskdrive (HDD), the heads 17 attached to the suspension assemblies 30 faceupper and lower surfaces of the magnetic disks 18, respectively. Thebase portion 60 of the FPC unit 21 is fixed to the bottom wall 12 a ofthe base 12.

FIG. 8 is a cross-sectional view showing a configuration example of themagnetic disk device 1 taken along line VIII-VIII shown in FIG. 6. InFIG. 8, only components required for a description are shown. In FIG. 8,a position of the center of the actuator assembly 22 or a rotationcenter position (hereinafter simply referred to as a rotation center) CGat which the actuator vibrates are shown. Here, the rotation centerincludes not only a point of application of a resultant force ofgravitational forces acting on the respective portions of an object, butalso a portion that can be considered as being substantially equivalentto the point of application. In addition, in FIG. 8, a distance Lx1between the rotation center CG and the sensor SR1 in an arrangementdirection Xa, a distance Lx2 between the rotation center CG and thesensor SR2 in the arrangement direction Xa, a distance Lz1 between therotation center CG and the sensor SR1 in the second direction Z, adistance Lz2 between the rotation center CG and the sensor SR2 in thesecond direction Z, and a distance Lh between the rotation center CG anda particular head 17 of the plurality of heads 17, for example, a head17 executing read or write processing, in the second direction Z areshown. As shown in FIG. 8, the actuator block 29 is supported bybearings 103 a and 103 b, and rotates around, for example, a referenceaxis AX0 passing through a pivot 100.

The sensor SR1 is located in an opposite direction to the sensor SR2with respect to the rotation center CG in the arrangement direction Xa.In addition, the sensor SR1 is located in an opposite direction to thesensor SR2 with respect to the rotation center CG in the seconddirection Z. The sensor SR2 is located at the cover side inside thehousing 10. The rotation center CG is detected by an analysis, or thelike, and is located on, for example, the reference axis AX0. It ispreferable that the sensors SR1 and SR2 are located at the same distancefrom the rotation center CG. That is, it is preferable that the sensorsSR1 and SR2 are located so as to be point-symmetrical to each other withrespect to the rotation center CG. In other words, it is preferable thatthe distance Lx1 and the distance Lx2 are the same as each other and thedistance Lz1 and the distance Lz2 are the same as each other.

In the example shown in FIG. 8, an estimated acceleration Ah of aparticular head 17 in the first direction X when the magnetic diskdevice 1 vibrates at a particular frequency due to a disturbance isrepresented by the following Equations:Ah1=1/(Lz1+Lz2)×(Lz2×A1+Lz1×A2)   Equation (1)Ah2=(A2−A1)×Lh/(Lz1+Lz2)  Equation (2)Ah=Ah1+Ah2  Equation (3).

Here, A1 is an acceleration detected by the sensor SR1, and A2 is anacceleration detected by the sensor SR2. In addition, Lh is a distancefrom the rotation center CG to the head 17 in the Z direction.

The estimated acceleration Ah of the head 17 executing the readprocessing or the write processing can be calculated by the aboveEquations (1) to (3).

FIG. 9 is a view showing an example of a positioning control system SYof the head 17 according to the first embodiment.

The control section 130 is electrically connected to the sensor SR1, thesensor SR2, and the like, through, for example, the board unit 21. Thecontrol section 130 calculates an estimated acceleration Ah of aparticular head 17, for example, a head 17 executing read processing orwrite processing based on the accelerations A1 and A2 detected by thesensor SR1 and the sensor SR2 and the above Equations (1) to (3). Thecontrol section 130 has a positioning control system SY for positioningthe head 17.

The positioning control system SY includes an MA controller 1311, an MAmodel 1312, an MA notch 1313, an MA 1314, a VCM controller 1321, a VCMnotch 1322, a VCM 1323, a compensator 1331, a manipulated variable C1, amanipulated variable C2, a manipulated variable C3, and a manipulatedvariable C4. Hereinafter, in the positioning control system SY, acontrol system of the VCM 24 may be referred to as a VCM control systemVSY, and a control system of the MA may be referred to as an MA controlsystem. The VCM control system VSY includes, for example, the VCMcontroller 1321, the VCM notch 1322, and the VCM 1323. The MA controlsystem MSY includes, for example, the MA controller 1311, the MA model1312, the MA notch 1313, and the MA 1314. The positioning control systemSY inputs the estimated acceleration Ah to the MA control system MSY,for example, the manipulated variable C2 located between the MAcontroller 1311 and the MA notch 1313, in a feed-forward manner.

The MA controller 1311 generates a signal (hereinafter, referred to asan MA control signal) corresponding to a control amount controlling theMA based on a position error signal (PES) PE.

The MA model 1312 generates a signal (hereinafter, referred to as anestimated MA driving signal) corresponding to the next driving amount ofthe MA estimated based on the MA control signal.

The MA notch 1313 suppresses resonance characteristics, and generates asignal (hereinafter, referred to as an MA driving signal) correspondingto a driving amount actually driving the MA.

The MA 1314 is driven based on the MA driving amount.

The VCM controller 1321 generates a signal (hereinafter, referred to asa VCM control signal) corresponding to a control amount controlling theVCM 24 based on the positioning error PE and the estimated MA drivingsignal.

The VCM notch 1322 suppresses resonance characteristics, and generates asignal (hereinafter, referred to as a VCM driving signal) correspondingto a driving amount actually driving the VCM 24.

The VCM 1323 is driven based on the VCM driving signal.

The compensator 1331 generates a signal (hereinafter, referred to as anestimated acceleration signal) obtained by cutting off a low frequencycomponent, a high frequency component, or the like, of the calculatedestimated acceleration Ah. The compensator 1331 includes, for example, afilter cutting off the low frequency component, the high frequencycomponent, or the like, of the estimated acceleration Ah, a doubleintegrator, an integer, transfer characteristics of the actuator for anacceleration sensor, and the like. The filter is, for example, a bandpass filter, and cuts off a low frequency component of about 1 kHz orless, a high frequency component of 10 kHz or more, or the like.

In the control section 130, when a target position of the disk 18 fromor to which data are read or written is specified, the manipulatedvariable C1 receives a reference value RF and a current particularposition of the head 17 (hereinafter, simply referred to as a currenthead position). The manipulated variable C1 outputs the positioningerror PE obtained by subtracting the current head position from thereference value RF to the MA controller 1311 and the manipulatedvariable C3.

The MA controller 1311 receives the positioning error PE. The MAcontroller 1311 outputs the MA control signal to the MA model 1312 andthe manipulated variable C2. The MA model 1312 receives the MA controlsignal, and outputs the estimated MA driving signal to the manipulatedvariable C3. The compensator 1331 receives the calculated estimatedacceleration Ah of the particular head 17, and outputs the estimatedacceleration signal to the manipulated variable C2. The manipulatedvariable C2 receives the MA control signal and the estimatedacceleration signal. The manipulated variable C2 outputs an MA controlsignal obtained by adding the estimated acceleration signal to the MAcontrol signal and suppressing an influence by vibrations of a specificfrequency, for example, a frequency of 4 to 9 kHz to the MA notch 1313.The MA notch 1313 receives the MA control signal, and outputs the MAdriving signal to the MA 1314. The MA 1314 is driven based on the MAdriving signal, and outputs a position of the MA (hereinafter, referredto as a MA position) to the manipulated variable C4.

The manipulated variable C3 receives the position error signal PE andthe estimated MA driving signal. The manipulated variable C3 outputs theposition error signal PE to which the estimated MA driving signal isadded to the VCM controller 1321. The VCM controller 1321 receives theposition error signal PE, and outputs the VCM control signal to the VCMnotch 1322. The VCM notch 1322 receives the VCM control signal, andoutputs the VCM driving signal to the VCM 1323. The VCM 1323 is drivenbased on the VCM driving signal, and outputs a position of the VCM 24(hereinafter, referred to as a VCM position) to the manipulated variableC4. The manipulated variable C4 outputs the target position (the currenthead position) of the particular head 17 obtained by adding the MAposition to the VCM position.

According to the present embodiment, the magnetic disk device 1 includesthe sensor SR1 disposed on the control circuit board 90, the sensor SR2disposed on the board unit 21, the VCM 24 (the VCM 1323), the MA (the MA1314), and the control section 130. The sensors SR1 and SR2 are locatedso as to be point-symmetrical to each other with respect to the rotationcenter CG. In addition, the sensors SR1 and SR2 may be arrangedsubstantially in parallel with the moving direction of the head 17. Thesensors SR1 and SR2 are disposed as described above, such that it ispossible to detect an influence on the head 17 when the magnetic diskdevice 1 vibrates at a specific frequency, without being affected byother resonance modes. The control section 130 calculates the estimatedacceleration Ah of the particular head 17 in the first direction X basedon the acceleration A1 detected by the sensor SR1, the acceleration A2detected by the sensor SR2, and the above Equations (1) to (3). Thecontrol section 130 inputs the calculated estimated acceleration Ah tothe MA control system MSY in a feed forward manner to control the MA,such that it is possible to suppress a positioning error of each head 17when the magnetic disk device 1 vibrates at a specific frequency, forexample, a frequency of 4 to 9 kHz due to a disturbance, for example, asound pressure. For this reason, in the magnetic disk device 1,positioning precision of each head 17 is improved.

In addition, with respect to a specific peak in the vicinity of about 2kHz at which the base and the disk vibrate due to a rotation harmoniccomponent (a component excited by magnetic force of the spindle motor)of the spindle motor, at least one of the accelerations A1 and A2 outputfrom the acceleration sensor SR1 on the PCB and the acceleration sensorSR2 on the base is applied separately from the estimated acceleration Ahto each head, a peak of a specific rotation harmonic component in thevicinity of about 2 kHz is calculated by the compensator 1331, and whenthe estimated acceleration is input to the MA control system MSY in thefeed forward manner so as to reduce the peak, the positioning accuracyof each head 17 is improved.

Next, a magnetic disk device according to a modified example will bedescribed. In the modified example, the same portions as those of theabovementioned embodiment will be denoted by the same referencenumerals, and a detailed description therefor will be omitted.

Modified Example

A magnetic disk device 1 according to a modified example is different ina configuration of a positioning control system SY from the magneticdisk device according to the abovementioned embodiment.

FIG. 10 is a view showing an example of a positioning control system SYof a head 17 according to a modified example.

The positioning control system SY further includes a compensator 1332and a manipulated variable C5. The positioning control system SY inputsan estimated acceleration Ah to a VCM control system VSY, for example, amanipulated variable C2 and the manipulated variable C5 located betweena VCM notch 1322, and a VCM 1323, in a feed-forward manner.

The compensator 1332 generates an estimated acceleration signal. Thecompensator 1332 includes, for example, a filter cutting off a lowfrequency component, a high frequency component, or the like, of theestimated acceleration Ah, a controller, an integer, transfercharacteristics of an actuator for an acceleration sensor, and the like.The filter is, for example, a band pass filter, and cuts off a lowfrequency component of about 1 kHz or less, a high frequency componentof 10 kHz or more, or the like.

A manipulated variable C3 receives a position error signal PE and anestimated MA driving signal. The manipulated variable C3 outputs theposition error signal PE to which the estimated MA driving signal isadded to a VCM controller 1321. The VCM controller 1321 receives theposition error signal PE, and outputs a VCM control signal to the VCMnotch 1322. The VCM notch 1322 receives the VCM control signal, andoutputs a VCM driving signal to the manipulated variable C5. Thecompensator 1332 receives a calculated estimated acceleration Ah of aparticular head 17, and outputs the estimated acceleration signal to themanipulated variable C5. The manipulated variable C5 outputs a VCMdriving signal obtained by adding the estimated acceleration signal tothe VCM driving signal and suppressing an influence by vibrations of aspecific frequency, for example, a frequency of 4 to 9 kHz to the VCM1323. The VCM 1323 is driven based on the VCM driving signal, andoutputs a position of the VCM 24 (hereinafter, referred to as a VCMposition) to the manipulated variable C4. The manipulated variable C4outputs a target position of the particular head 17 obtained by addingan MA position to the VCM position.

According to the modified example, the magnetic disk device 1 inputs thecalculated estimated acceleration Ah to the VCM control system VSY in afeed forward manner to control the VCM 24, such that it is possible tosuppress an influence on a positioning error of each head 17 when themagnetic disk device 1 vibrates at a specific frequency, for example, afrequency of 4 to 9 kHz due to a disturbance, for example, a soundpressure. For this reason, in the magnetic disk device 1, positioningprecision of each head 17 is improved.

In addition, with respect to a specific peak in the vicinity of about 2kHz at which the base and the disk vibrate due to a rotation harmoniccomponent (a component excited by magnetic force of the spindle motor)of the spindle motor, at least one of the accelerations A1 and A2 outputfrom the acceleration sensor SR1 on the PCB and the acceleration sensorSR2 on the base is applied separately from the estimated acceleration Ahto each head, a peak of a specific rotation harmonic component in thevicinity of about 2 kHz is calculated by the compensator 1331 and thecompensator 1332, and when the estimated acceleration is input to aposition of the VCM 24 and the MA control system MSY in the feed forwardmanner so as to reduce the peak, the positioning accuracy of each head17 is improved.

A case in which a low-density gas (an inert gas) (for example, helium)having a density lower than that of air is enclosed in the housing 10 isdescribed, but the configurations of the abovementioned embodiment andthe modified example can also be applied to a general magnetic diskdevice in which an inert gas is not enclosed. The general magnetic diskdevice has, for example, a structure in which the upper end opening ofthe base 12 is closed with one top cover rather than two covers such asthe inner cover 14 and the outer cover 16.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the inventions. Indeed, the novel embodiments described hereinmay be embodied in a variety of other forms; furthermore, variousomissions, substitutions and changes in the form of the embodimentsdescribed herein may be made without departing from the spirit of theinventions. The accompanying claims and their equivalents are intendedto cover such forms or modifications as would fall within the scope andspirit of the inventions.

What is claimed is:
 1. A magnetic disk device comprising: a housing that comprises a base that comprises a bottom wall and side walls standing along a circumference of the bottom wall, and a cover facing the bottom wall and closing the base; an actuator assembly that is housed inside the housing and is rotatable around a rotation axis; a head movably supported by the actuator assembly; a control circuit board provided outside of the housing; a first sensor disposed on the control circuit board; a second sensor disposed inside the housing; and a fixed portion fixed in the housing, wherein the fixed portion comprises a protrusion portion that protrudes in a height direction from the bottom wall toward the cover inside the housing, the protrusion portion has an upper surface positioned the cover side in the height direction, and the second sensor is located on the upper surface.
 2. The magnetic disk device according to claim 1, wherein the fixed portion is fixed to the bottom wall and is provided a first wiring electrically connecting the actuator assembly and the control circuit board to each other.
 3. The magnetic disk device according to claim 2, wherein the fixed portion is provided a second wiring electrically connecting the control circuit board and the second sensor to each other.
 4. The magnetic disk device according to claim 1, wherein the first sensor is located in a first region of the control circuit board fixed to outside of the bottom wall by a first screw, and the second sensor is located in a second region of a member fixed to the upper surface by a second screw.
 5. A magnetic disk device comprising: a housing that comprises a base that comprises a bottom wall and side walls standing along a circumference of the bottom wall, and a cover facing the bottom wall and closing the base; an actuator assembly that is housed inside the housing and is rotatable around a rotation axis; a head movably supported by the actuator assembly; a control circuit board provided outside of the housing; a first sensor disposed on the control circuit board; and a second sensor disposed inside the housing, wherein the first sensor and the second sensor are arranged on a straight line passing through the rotation axis, the first sensor is located in an opposite direction to the second sensor with respect to a center of the actuator assembly in a height direction from the bottom wall toward the cover, and the second sensor is located at the cover side in the height direction.
 6. The magnetic disk device according to claim 5, further comprising a fixed portion fixed in the housing, wherein the fixed portion comprises a protrusion portion that protrudes in the height direction, and the second sensor is provided on the protrusion portion.
 7. The magnetic disk device according to claim 6, wherein the protrusion portion has an upper surface positioned the cover side in the height direction, and the second sensor is located on the upper surface.
 8. The magnetic disk device according to claim 7, wherein the fixed portion is fixed to the bottom wall and is provided a first wiring electrically connecting the actuator assembly and the control circuit board to each other.
 9. The magnetic disk device according to claim 8, wherein the fixed portion is provided a second wiring electrically connecting the control circuit board and the second sensor to each other.
 10. A magnetic disk device comprising: a housing that comprises a base that comprises a bottom wall and side walls standing along a circumference of the bottom wall, and a cover facing the bottom wall and closing the base; an actuator assembly that is housed inside the housing and is rotatable around a rotation axis; a head movably supported in a movement direction by the actuator assembly; a control circuit board provided outside of the housing; a first sensor disposed on the control circuit board; a second sensor disposed inside the housing; and a fixed portion fixed in the housing, wherein the first sensor and the second sensor are located on opposite sides in a height direction from the bottom wall toward the cover, the second sensor is located on the fixed portion.
 11. The magnetic disk device according to claim 10, wherein the first sensor detects a first acceleration in the movement direction.
 12. The magnetic disk device according to claim 11, wherein the second sensor detects a second acceleration in the movement direction.
 13. The magnetic disk device according to claim 12, wherein the fixed portion comprises a protrusion portion that protrudes in the height direction from the bottom wall toward the cover inside the housing, the protrusion portion has an upper surface positioned the cover side in the height direction, and the second sensor is located on the upper surface. 